Carbon dioxide is a gas but carbon can also be found in solid form (coal) and liquid form (oil). Carbon based fuels are fossils extracted from the Earth's interior. The minerals, rocks and land formations below and on the Earth's surface are called the geosphere. These fossilized deposits were created millions of years ago when plants and animals died and were compacted and preserved by geologic processes. Coal, oil and natural gas are the product of these geological processes and when we burn these fuels to create electricity or heat we release the chemicals like carbon dioxide and methane into the atmosphere, both of which are greenhouse gases.
Hydrosphere
Water plants, like algae and phytoplankton absorb carbon dioxide. The carbon dioxide is originally absorbed into the water column and aquatic plants draw the carbon dioxide from the water. In fact, 70% of the Earth's surface is covered with water and is called the hydrosphere. The oceans, seas, lakes, ponds, rivers and streams are huge carbon sinks, meaning carbon sinks into them and is stored for a long period of time. Ocean acidification occurs when too much carbon is absorbed into the water column making oceans acidic which decreases ecosystem sustainability. Coral reefs are being destroyed because the acidic water inhibits the production of calcium necessary for coral development.